Photodetector array's are becoming increasingly important in lightwave communication systems due to parallel optical data links and wavelength division multiplexing. For example, photodetector arrays are employed in photospectrometers to read out the spectrum generated by a dispersive medium such as a grating. In these contexts, the array is typically one-dimensional. However, the functionality of these linear detector arrays is effected by the presence of bad detectors. For fiber optic communication at a wavelength of 1.55 .mu.m, 1.times.12 arrays of InGaAs/InP photodiodes have been fabricated and substantially uniform 1.times.12 arrays have been demonstrated. In addition, 1.times.512 arrays have been demonstrated with a reported yield that was approximately 98%. In the latter case, bad devices were found to be almost exclusively leaky, and usually caused by a defect in the epitaxial growth of the devices. That is, microscopic point defects that occurred during fabrication resulted in devices that exhibited excess photodiode leakage. As a consequence, defects which result in shorts and opens are a primary limitation on device yield.
Fabrication of two-dimensional arrays integrated with Si CMOS to form arbitrary circuit formations have been demonstrated. The integration technology utilized in fabricating these devices was flip-chip bonding. As a consequence, the size of the array is fairly unrelated to the difficulty in fabricating the chip, and thus a chip can have for example, as many as 10,000 elements. Arrays of GaAs/AlGaAs photodiode/modulators operating at 850 nm and having as many as 4,352 elements have been produced. The yield of these devices were measured to be approximately 99.95%. This result is presumably due to the higher quality of GaAs/AlGaAs material than InGaAs/InP material.
Accordingly, there is a need to provide a simple and effective apparatus and method which improves device functionality and uniformity by utilizing photodiode redundancy in detector arrays.